1. Field of the Invention
The present invention relates to a driving force switching control apparatus applied to a four-wheel drive vehicle which has at least one power source and performs two-wheel or four-wheel drive running according to the running state of the vehicle.
Priority is claimed on Japanese Patent Application No. 2004-033973, filed Feb. 10, 2004, the content of which is incorporated herein by reference.
2. Description of the Related Art
Recently, in order to improve fuel efficiency, four-wheel drive vehicles having at least one power source and performing two-wheel or four-wheel drive running according to the running state of the vehicle have been developed. As a relevant technique, Japanese Unexamined Patent Application, First Publication No. Hei 07-231506 discloses a hybrid vehicle having an engine and a motor as driving sources, and a charging device for charging a power source for the motor by using rotation of the engine, in which when measured remaining charge of the power source is equal to or less than a specific value and the engine is in a low load state, the load on the engine is increased to a maximum efficiency range so as to improve the charge efficiency in charging using the charging device. As another relevant technique, Japanese Unexamined Patent Application, First Publication No 2003-312295 discloses determining whether a vehicle runs at a constant speed (i.e., performs cruise running). If it is determined that the vehicle performs cruise running, the drive system is switched to two-wheel drive running.
However, even in the cruise running, two-wheel drive may not give adequate driving force depending on road surface conditions. If switching to two-wheel drive is executed even in such a case, a slip may occur on acceleration or deceleration of the vehicle, thereby degrading running performance (i.e., driveability).